Gavin Newsom, the frontrunner in next month's California primary race, is up with a new ad targeting one of his fellow Democrats — John Chiang. 

The ad claims that Chiang, who previously served as state treasurer and state controller, "lost track of $31 billion" during his stint as controller. 

Recent polling has shown the race for second place in flux over the past weeks, with Republicans John Cox and Travis Allen in the mix along with other Democrats jockeying for position. 

Chiang has spent about $1.7 million on California airwaves — behind Newsom's $6.1 million and nearly $12 million spent by a super PAC backing Democrat Antonio Villaraigosa. 

In a release, Chiang's campaign called the attack "false and erroneous" and said that the latest volley from Newsom is evidence that Chiang is gaining public support. 

“Gavin Newsom’s desperate attempt to attack John's record is evidence that John is gaining momentum, and that Gavin is scared to confront his biggest one-on-one threat this November,” said Fabien Levy, Deputy Campaign Manager and Communications Director for John Chiang’s campaign. “These dirty attacks show Gavin lacks the integrity to be governor and can't be trusted to tell the truth."

Newsom has suggested that he would prefer to face a Republican in the general election after the state's top-two nonpartisan primary in June. 

You can view the ad here. According to ad trackers at Advertising Analytics, it began airing Monday in major California markets.